This invention relates to removal of the epithelium during medical treatment of the eye.
The cornea comprises transparent avascular tissue that forms the anterior portion of the eye. It resides in the sclera at the limbus. The cornea functions as both a protective membrane and a "window" through which light passes as it proceeds to the retina. The transparency of the cornea is due to its uniform structure, avascularity, and deturgescence, which is the state of relative hydration of the corneal tissue. The average adult cornea is about 0.65mm thick at the periphery and about 0.54 mm thick in the center. From anterior to posterior, the cornea has the following five distinct layers: the epithelium, Bowman's membrane, the stroma, Descemet's membrane, and the endothelium. The present invention concerns the epithelium, Bowman's membrane and the stroma. The epithelium consists of five or six layers of cells, and the underlying Bowman's membrane, a clear acellular layer, is a modified portion of the stroma. The corneal stroma accounts for about 90 percent of the corneal thickness. The stroma is composed of intertwining lamellar fibers that are about 1 .mu.m wide and run almost the full diameter of the cornea. They run parallel to the surface of the cornea and by virtue of their size and periodicity are optically clear.
The corneal epithelium encompasses a rich network of nerve fibers with bare ends. Whenever the nerve fibers are exposed, they produce a sensation of pain. Since the endings of the nerve fibers are located near the surface, severe pain results from even a minor abrasion of the corneal epithelium. The nutrition of the cornea including the epithelium is provided by the vessels of the limbus, the aqueous, and tears. The corneal epithelium also extracts most of its oxygen from the atmosphere.
Damage to the epithelium causes transient localized swelling of the corneal stroma that clears when the epithelium cells regenerate. The epithelium forms an effective barrier to the entrance of microorganisms into the cornea. If the epithelium is removed or traumatized, Bowman's layer and the avascular stroma become susceptible to a variety of microorganisms.
The epithelium layer consists of highly renewable cells which are capable of regrowth within a few days. Once formed, these cells define a highly organized light transparent unit.
Before any surgical procedure on the stroma can be conducted, the epithelium must first be removed. The surgical removal of the epithelium is currently performed by mechanically scraping the epithelium layer from the underlying layer. The precision and quality of this procedure depends upon the ophthalmologist's skill and also on the morphology of the eye surface, i.e., how firmly the epithelium is attached to Bowman's membrane and to the stroma and the health and condition of the epithelium. In particular, contact lens wearers and people who previously have undergone corneal sculpting often have the epithelium strongly attached to the underlying surface. Patients who have undergone prior injury or treatment might often have scar tissue. In such cases, mechanical epithelium removal is frequently non-uniform and requires considerable time to perform. Furthermore, since the procedure depends on the skill of the ophthalmologist, removal of the epithelium entails risk of damage to the Bowman's layer and to the stroma.
After eye surgery, it often takes 40 to 70 hours for the missing epithelium layer to regrow over the surface of the eye. It takes even longer for the epithelium cells to achieve coherent orientation and organization that allows full transparency and proper vision. This is not only a painful process, but the patient's vision is also impaired during this healing period.
It has been suggested that de-epithelization of the eye be performed using scraping or tearing by mechanical means, with or without the additional use of softening agents. However, with such techniques the epithelium is not removed uniformly and in any event the healing period and discomfort can remain a problem. It has also been suggested to replace removed epithelium cells back upon the eye after the eye surgery to assist in healing, but we are unaware that this has been done satisfactorily.
In summary, there continues to be a need for a surgical device and procedure which can remove the epithelium in a standardized manner, very quickly and without causing damage to the cornea and which enables rapid convalescence. In addition, there is a particular need for a device and procedure that enables removal of the epithelium which is strongly attached to the underlying layer, i.e., Bowman's membrane or stroma in cases wherein the Bowman's membrane was previously removed.